Wireless communication systems are attempting to reduce noise and interference among wireless devices and base stations by narrowing the width of the wireless communication beams. These systems further attempt to direct or steer these narrow beams at predefined regions or at intended mobile devices. The narrower beam interferes with fewer non-intended mobile devices or other sensitive devices. This additionally can allow the beam to be transmitted at reduced power levels because the beam covers a smaller area. A reduction in the transmitted power can also reduce the average interference at non-intended devices.
Some wireless communications systems require detailed channel information to determine and maximize a signal-to-noise ratio at intended mobile devices. For a time-division duplex (TDD) system, reciprocity can be assumed between the propagation channels on the forwards and reverse link so that the detailed channel information is available at the transmitter. However, for frequency-division duplex systems (FDD), reciprocity does not apply between the forward and reverse links, and thus detailed channel information is not available unless channel measurements are taken at the receiver and fed back to the transmitter. Additionally, many existing systems utilize common pilot signals to demodulate the received traffic signals. In these systems, the mobile estimates the channel gain and phase using the common pilot signal, makes the assumption that the channel for the common pilot signal is the same as for the traffic channel, and uses the gain and phase estimate from the common pilot channel to demodulate the traffic channel signals. These assumptions cannot be utilized when a system uses separate beams for the common pilot signal and for each traffic user. The accurate implementation of narrower beams appears to offer potentially significant benefits. However, problems with previous systems potentially prevent and/or potentially inhibit the implementation of beam narrowing. Additionally, the explicit and detailed channel information required by previous systems will reduce reverse link capacity if fed back from the receiver, while the circuitry and significant signal processing capabilities to calculate the beams can be expensive to implement. These costs and added complexity may possibly serve to delay or deter implementation of narrowed beam systems.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.